1. Field of the Invention
The present invention relates to an ion implantation method and ion implantation apparatus and, more particularly, to a technology of controlling the implant angle distribution of an ion beam.
2. Description of the Related Art
In a semiconductor manufacturing process, the process of implanting a semiconductor wafer with ions (hereinafter, also referred to as “ion implantation process”) is generally performed for the purpose of changing the conductivity of the semiconductor, changing the crystal structure of the semiconductor, etc. Apparatuses used in the ion implantation step are called ion implantation apparatuses. Ion implantation apparatuses are provided with the function of generating ions by using an ion source and forming an ion beam by accelerating the generated ions, and the function of transporting the ion beam to the implantation processing chamber and irradiating a wafer in the chamber with the ion beam. For the purpose of implanting the entire surface of the wafer subject to processing, the ion beam is reciprocally scanned by a beam scanner and the wafer is reciprocally moved in a direction perpendicular to the direction of beam scan.
It is known that when the angle of the ion beam incident into the wafer is changed, the mode of interaction between the ion beam and the wafer is changed, affecting the processing result of ion implantation. For example, an ion beam incident along a crystal axis or crystal plane of the wafer results in a channeling phenomenon in which implanted ions reach deeper into the wafer from the beam incident surface than otherwise, affecting the carrier concentration distribution inside the wafer obtained as a result of the implantation process. In this background, methods for controlling the incident angle of an ion beam used in the implantation process are proposed.
Angle characteristics of an ion beam incident on a wafer include angle distribution of ion particles forming the ion beam as well as average incident angle of the ion beam as a whole. An ion beam incident on a wafer may diverge or converge slightly. Thus, the ion particles forming the beam have an angle distribution with a certain spread. If the angle component of some of the ion particles with deviation in the incident angle meets a channeling condition, a channeling phenomenon due to those ions occurs, even if the average incident angle of the beam as a whole does not meet the channeling condition. Conversely, if the angle component of some the ion particles with deviation in the incident angle does not meet the channeling condition, a channeling phenomenon due to those ions is inhibited, even if the average incident angle of the beam as a whole meets the channeling condition. It is therefore necessary to control the beam angle distribution precisely in order to control the shape and range of carrier concentration distribution formed in the wafer precisely.